“World’s Greatest Dogs”—part of Nat Geo WILD’s Barkfest weekend—has, despite its title, nothing to do with dog heroes of polar expeditions and such. Here we have heroes of another kind, canines who’ve usually been rescued from some unspeakable early life to become champion athletes. The sort shown doing impossible things—running jumps from rooftops to the arms of an owner-trainer as Jumpy (a Border Collie-Australian Cattle Dog mix) does. The 38-pound star is now acknowledged to be the world’s fastest dog-skateboarder. He’s not the only canine here whose prowess will keep your eyes glued to the screen. There’s Nakio, called the bionic dog—he has four artificial legs—whose skills are as formidable as his dauntless spirits.